Producers may wish to house more pigs than normal in a pen in the immediate post weaning period in order to reduce heat and space requirements. The effect of this practice on productivity and behaviour may differ depending on group size used. In addition, housing pigs at reduced space allowances in the immediate post weaning period may lead to a requirement to expand pens or, more realistically, to split groups as the pigs get larger. This study assessed the effects of group size and space allowance during the initial post weaning period, and of expanding pens or splitting groups during the second half of the post weaning period, on productivity and behaviour of pigs.